What Is the Longest River in the World?

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iStock

The answer to the question “What’s the longest river in the world?” might sound simple—find the source, the mouth, and measure—but in between those steps are strange definitions, fractals, hydrology, and especially national pride. It’s an issue so complicated that several hydrologists contacted by Mental Floss explained that river length isn't even considered a useful measure anymore. So, what is the longest river in the world?

HOW LONG IS A RIVER?

According to Laurel Larsen, assistant professor at the University of California Berkeley’s geography department, “The length of a particular river is the longest possible along-thalweg continuous distance from the headwaters (1st order stream) to the mouth of a river.”

To unpack those terms, the thalweg is “the line connecting the lowest or deepest points along a stream bed or valley.” First order stream is more complicated. There are two major ways to classify stream order, but the most common is the Strahler method. In this method, streams without any tributaries entering—streams that are just starting out the river—are first order. When two first order streams join together they form a second order stream, and when two second order streams join they form a third order (but if a first order stream intersects with a second order, the main river stays a second order stream).

The source of a river then is considered to be the furthest distance to the source of a stream that has no inputs—although, in practice, this can be extremely difficult to determine. And it's not a perfect system. (For historical reasons, the source of the Mississippi is often treated separately from the Missouri, despite the conventional definition grouping them into one river system.)

As for the mouth? That’s also contentious. For some rivers, the mouth is relatively simple to determine. But for large rivers entering the ocean, like the Amazon, where the mouth is placed can make all the difference.

ARE WE GOING TO ANSWER THE QUESTION?

The longest river has generally been the Nile, with the Amazon coming in second. But in 2007 Brazilian scientists announced that a new analysis put the Amazon on top. They got this by identifying a new source, but more importantly a new mouth. Traditionally, the mouth of the Amazon has been located on the north side of Marajó Island. But this new report wrapped the river around the south side of the island to the Pará River and then out into the ocean.

What side of an island the mouth is on might not seem relevant, but Marajó Island is the size of Switzerland. The new source plus the new mouth gave a distance longer than the Nile.

This was controversial. The Pará River is usually associated with the Tocantins River, not the Amazon. And more recent studies have tended to agree that, although there is some Amazon water in it, the Pará is distinct from the Amazon. Which means that the current best guess for the longest river in the world is still the Nile.

But there’s another, more fundamental issue with measuring a river: What does length even mean?

SO WHAT’S THE PROBLEM?

The early 20th century mathematician Lewis Fry Richardson made the observation that Spain and Portugal disagreed on their border length. Spain said it was 987 km and Portugal maintained it was 1214 km. The disagreement wasn’t down to disputed territories or anything like that; Richardson explained that it was the length of the measuring stick. As the measuring stick gets smaller, it’s able to more accurately capture the curves and nuances of bends and curves in complex borders.

The same trick appears with rivers. Rivers meander and have small curves. And if you zoom in further, more little bends and twists might appear in the thalweg.

It’s called the coastline paradox—the length of something complex is basically impossible to determine because the length keeps increasing the smaller the measurement goes.

For both this reason and the inherent difficulties of determining length, several researchers have told Mental Floss that river length just isn’t something that particularly matters, and what is really important is drainage area, which is the area of land that contributes water to the river. Unlike river length, a few elevation measurements make this a much easier metric to calculate. And according to an article in Nature, using this metric, the Amazon is dramatically the largest river in the world, with a drainage area of 6.3 million square kilometers. If it were a country, the drainage basin would be the seventh largest in the world just behind Australia.

The Nile falls down to fifth, behind the Congo, the Mississippi, and the Ob. So in the measurement that matters to hydrologists today, the Amazon wins it.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

Why Are Poinsettias Associated with Christmas?

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iStock

Certain Christmas traditions never seem to go out of style. Along with wreaths, gingerbread cookies, and reruns of A Christmas Story sits the poinsettia, a red-tinged leafy arrangement that’s become synonymous with the holiday. Upwards of 100 million of them are sold in the six weeks before December 25.

Why do people associate the potted plant with seasonal cheer? Chalk it up to some brilliant marketing.

In 1900, a German immigrant named Albert Ecke was planning to move his family to Fiji. Along the way, they became enamored of the beautiful sights found in Los Angeles—specifically, the wild-growing poinsettia, which was named after Joel Roberts Poinsett, the U.S.-Mexican ambassador who first brought it to the States in 1828. Ecke saw the appeal of the plant’s bright red leaves that blossomed in winter (it’s not actually a flower, despite the common assumption) and began marketing it from roadside stands to local growers as "the Christmas plant."

The response was so strong that poinsettias became the Ecke family business, with their crop making up more than 90 percent of all poinsettias sold throughout most of the 20th century: Ecke, his son Paul, and Paul’s son, Paul Jr., offered a unique single-stem arrangement that stood up to shipping, which their competitors couldn’t duplicate. When Paul III took over the business in the 1960s, he began sending arrangements to television networks for use during their holiday specials. In a priceless bit of advertising, stars like Ronald Reagan, Dinah Shore, and Bob Hope were sharing screen time with the plant, leading millions of Americans to associate it with the holiday.

While the Ecke single-stem secret was eventually cracked by other florists—it involved grafting two stems to make one—and their market share dwindled, their innovative marketing ensured that the poinsettia would forever be linked to Christmas.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

Why Does Santa Claus Live at the North Pole?

allanswart/iStock via Getty Images
allanswart/iStock via Getty Images

As children settle in for a restless night’s sleep this Christmas Eve, they’ll no doubt be picturing Santa Claus on his way from the snowy ’scapes of the North Pole to deliver them Star Wars LEGO sets, Frozen 2 dolls, and everything else on their wish list. They picture Santa at the North Pole, of course, because they’ve seen him living there in numerous Christmas movies, books, and television specials, from perennial Rankin/Bass programs to more modern classics like 2003’s Elf.

While it might seem a little more magical if we told you that nobody really knows why Santa lives there, there is a relatively traceable paper trail: The first known reference to Santa’s North Pole residence is in an 1866 cartoon from Harper’s Weekly.

According to Smithsonian.com, famed political cartoonist Thomas Nast—who was also responsible for establishing the donkey and elephant as the symbols for the Democratic and Republican parties, respectively—first started creating Harper’s Weekly Christmas cartoons as Union propaganda for the Civil War in January 1863. Borrowing imagery from Clement Clarke Moore’s (alleged) 1823 poem “A Visit From St. Nicholas” (which you’d probably recognize as “’Twas the Night Before Christmas”), Nast developed the white-bearded, rosy-cheeked, all-around jolly guy that we know today, and showed him passing out gifts to Union soldiers, climbing into a chimney as a soldier’s wife prays, and more.

harper's weekly santa claus at camp by thomas nast
Thomas Nast, Harris Brisbane Dick Fund, Wikimedia Commons // Public Domain

The cartoons became so popular that Nast branched out from his source material and began inventing his own details to add to Saint Nick—like where he’s from, for example. A December 29, 1866 issue of Harper’s Weekly debuted a multi-image cartoon titled “Santa Claus and His Works,” which includes a small inscription along the circular border that reads Santa Claussville, N.P. According to The New York Times, we don’t know exactly why Nast chose the North Pole (or if it was even his own idea), but there are a few reasons it made sense for the time period.

For one, Santa Claus was already widely associated with snow because most of the publishing companies producing Christmas cards and other content were located in New England, where it actually snows around Christmas. Furthermore, the 1840s and 1850s were partly characterized by high-profile—and ill-fated, in the Franklin expedition's case—attempts to explore the Arctic, and the public was generally interested in the mysterious, poorly-charted region. Because the Pole was unoccupied, Santa and his elves could toil the year away without interference from prying eyes; and, because it was unclaimed, Santa could remain a bastion of benevolence for every nation.

merry old santa claus by thomas nast
"Merry Old Santa Claus," perhaps Nast's most famous illustration of Santa, from the January 1, 1881 edition of Harper's Weekly.
Thomas Nast, Wikimedia Commons // Public Domain

Though we’ll likely never know Nast’s personal rationale behind placing Santa Claus in the North Pole, one thing’s for sure: At this point, it’s hard to imagine him living anywhere else. It’s also hard to imagine him riding a broom, wielding a gun, or smoking cigarettes (find out the stories behind those early Santas here).

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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